Tuesday, November 06, 2012

Did Your Soybean Yield Also Suffer From SCN This Year?

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When you harvested soybeans this fall, did your yield monitor make some wide swings as you moved through the field? Part of the problem was due to the drought and soil type, but part of the problem may have resulted from soybean cyst nematode (SCN) in your field. Although you could not do much to control what yield loss was due to the drought, SCN’s role in your lower revenue may have been preventable to a significant degree. Plan this winter to recapture those lost dollars.

SCN has been robbing yields for most soybean producers around the Cornbelt, and there is no better time than the present to reverse that trend, say Ohio State University plant pathologists Anne Dorrance and Terry Niblack. The specialist say high populations of SCN can create huge yield losses, particularly when soybean varieties are planted that are susceptible to their attack on roots.

Unfortunately, since SCN operates below the soil the problem usually is not detectable until harvest time the soybeans do not fill your grain tank as fast as you would have expected. They will be in pockets in the field, especially in no-till fields say Dorrance and Niblack. They report that within a 25-foot span the level of eggs per cup of soil can range from zero to 2,000, and at that point yield losses are measurable. They advise producers to look at the low yield spots in a soybean field and target those areas to sample the soil and begin monitoring the potential problem you have on your entire operation to ensure it does not get out of control and soybean profitability plunges.

SCN resistance within soybean varieties comes from a variety known as PI 88788, but since that has been the dominant source of resistance and has been used for many years, its resistance is wearing down, just like waterhemp and marestail are becoming resistant to glyphosate. Dorrance and Niblack report that some populations of SCN in Ohio are feeding on the roots of soybean plants with the PI 88788 genetics. That means even users of soybean varieties that are supposedly resistant the SCN should begin to monitor SCN populations in their fields.

Nasty, unexpected surprise

The SCN specialists say they have found some fields where SCN populations are more than 10,000 per cup of soil, and producers took their advice to not plant soybeans in those fields for several years in an effort to starve the SCN down to more manageable levels. However, after 3 years of no soybeans, the first crop was still severely damaged by SCN even though the field was planted with a variety that was considered to be resistant. After harvest, soil samples were taken again and SCN populations were still considered too high. Even though the field was in Ohio, similar cases have been reported in Missouri and Iowa where that research was also done. The outcome of the research points to the need to keep populations low, since high populations cannot be reduced.

Suggested control measures

Rotate the field with non-soybean crops.

Keep weeds under control which also provide food over the winter.

Plant varieties with the best SCN resistance genetics.

Sample the soil in areas of low yield to find out your level of SCN population.

Suggested strategy

If soil samples show non-detectable levels, and you have a 3-year rotation without double-cropping wheat and soybeans, then sample every 20 years.

If you have non-detectable levels with a 3-year rotation, and you do double crop wheat and soybeans, then sample every 10 years.

If you have non-detectable levels and you have a two year rotation of corn and soybeans, sample every 10 years.

If your SCN populations are 40 to 2,000, and you rotate soybeans with corn and wheat, sample every 5 years.

If SCN populations are 40 to 2,000, and you plant only soybeans, sample every year.

If SCN populations are over 2,000, sample every year.

Fall is the best time to sample since it provides an opportunity for the lab to provide a report before you turn in your seed order for the following year. How do you sample a field? Iowa State University SCN nematode specialist Greg Tylka provides a 9-minute YouTube video of sampling both soybean and corn fields for SCN populations.

Summary:

Soybean cyst nematode (SCN) may have been consuming a good portion of your soybean yield if you noticed spots in your field where yields were much lower than others, but problems were not detectable during the growing season. SCN is now becoming resistant to soybean varieties that have been bred for resistance to SCN. Both rotation with other crops and soil sampling should be done regularly to monitor population levels.